This invention relates to measuring devices for lenses and, more particularly, to devices for accurately determining the height of the pupil from the lower lens recess edge of an eyeglass frame.
In order to properly fit multifocal glasses, it is necessary to measure the distance from the lower inside edge of the frame to the center of the pupil as illustrated in FIG. 1. This figure includes a frame 101, a lower inside edge of the frame 102, an eye pupil 105 with its center at 103 and a distance d (104) from the lower inside edge of the frame to the center of the pupil. Where there is no lower frame this measurement is understood as being made from the lower edge of the lens.
This measurement is currently accomplished by merely placing a millimeter scale against the frame and making a rough estimate of the center of the pupil. Such an approach is illustrated in FIG. 2. This Figure shows the frame 101, the pupil 105 and a millimeter scale 201 with the scale in position to make the pupil height measurement. Measurements of this sort are subject to a number of errors caused by such factors as nonhorizontal alignment between the operator's or optician's eye and that of the patient, and improper measurement of both the lower edge of the frame and the center of the pupil due to parallax.
Some improvement is provided by a clear plastic gage which is designed to be positioned with its lower edge resting on the lower edge of the frame as shown in FIG. 3 to eliminate alignment or parallax errors for the pupil.